The level of maternal phenylalanine which will maintain a normal pregnancy. At what stage of pregnancy a low phenylalanine diet is most effective in preventing the effects of maternal PKU on the developing fetus. If the beneficial effects of a low phenylalanine diet can be improved when initiated prior to conception compared to post-conception. Whether the diet reduces the frequency of mental retardation, spontaneous abortions, low birth weight,congenital malformations, neurological and behavioral impairment found in infants of mothers with hyperphenylalaninemia.The levels of tyrosine and trace metals during pregnancy and ascertain the effects of supplementation if levels are found to be low on pregnancy outcome.